1. Field of the Invention
The present invention relates to a phase shifter, and in particular, to an inline phase shifter.
2. Background Information
A first type of phase shifter is an electrically reactive structure in which electrical reactive properties are altered by applied voltages or by changing the relation between electrically reactive elements. U.S. Pat. No. 5,309,166 to Collier et al., hereby incorporated by reference, discloses a phase shifter in which electrical reactive properties are altered by applied voltages. U.S. Pat. No. 5,504,466 to Chan-Son-Lint et al., hereby incorporated by reference, discloses a phase shifter in which electrical reactive properties are altered by changing the relation between electrically reactive elements with a piezoelectric element.
A second type of phase shifter is a delay type phase shifter that uses a switch to switch between signal paths in combination with electrical reactive elements. U.S. Pat. No. 6,184,827 to Dendy et al., hereby incorporated by reference, discloses a phase shifter in which the signal path is altered by changing the length of the signal path with a MEMS switch to switch between lengths of transmission line.
The first and the second types of devices can phase shift a signal within a range of phases but inherently degrade the signal strength because of power losses due to electrical resistances.
A third type of phase shifter is a fixed waveguide having fixed dimensions in terms of the cross-sectional area of the waveguide path through the waveguide and the length of the waveguide. The fixed waveguide can phase shift a signal with minimal signal strength degradation. However, a fixed waveguide can only phase shift a signal to one predetermined phase based on the physical dimensions of the waveguide.